In-situ Formation Of Hydroxyapatite By Micro-arc Oxidation And Effect Of Particles-doping On The Properties Of Coatings

Titanium and its alloys are expected to be ideal materials for medical application because of its biocompatibility,high corrosion resistance and bio-stability.However,unlike bioactive ceramics,bio-glass,hydroxyapatite(HA),titanium implants have low bioactive and cannot bond directly to the bone.Various surface modification approaches have been used for biological properties improvement.Among various surface modification techniques,micro-arc oxidation(MAO),which can produce porous,adhesive and bioactive coatings,has aroused considerable attention.Generally,the titanium oxide layer can further crystallized into HA through a hydrothermal treatment or alkali heat-treatment.Few studies prepared HA coating by micro-arc directly.In this study,we aim to prepare HA containing coatings on titanium by adjusting the electrolytes.In this study,calcium acetate(CH3COO)2Ca)as the calcium compound,disodium hydrogen phosphate(Na2HPO4),sodium hexametaphosphate((NaPO3)6),sodium phosphate(Na3PO4),disodium glycerophosphate(C3H4Na2O6P-5H2O)four different phosphate salts as phosphate compounds,which were chosen to prepare 12different groups electrolytes.The microstructure,corrosion resistance and biological activity were studied.An optimization electrolyte will be used as the basis electrolyte for further study.Then,explore the influence of particles adding(CaHP04-2H2O and Ca10(PO4)6(OH)2)on the MAO coating properties.Structure,physical and chemical properties of MAO coatings prepared by different electrolytes are characterized by X-ray diffraction(XRD),scanning electron microscope(SEM),Fourier transform infrared spectroscopy(FT-IR)and electrochemical characterization workstation.The apatite inducing property in SBF is characterized by using SEM,EDS,XRD and FT-IR.The results showed that only by micro-arc oxidation technology directly can prepared(Ca1o(PO4)6(OH)2-XFX))containing coatings.When(CH3COO)2Ca as the calcium salt,Na2HPO4 and(NaPO3)6 as a phosphate salt,calcium and phosphorus ratio of 3:1,apatite coatings can be prepared directly.The coatings have a high content of calcium and phosphorus,and have a good ability in apatite inducing in SBF for 7 days.Round-shapes deposition with a diameter of microspheres of 6 ?m can be observed in micro-holesl.Thickness increases with the increasing of phosphorus concentration.The main phases are Anatate,Rutile,CaF2 and CaTiO3,and the fluorine-containing phase appeared in the late period of micro-arc oxidation process.C3H7Na2O6P·5H2O does not have good biological activity in SBF.Though biological active is bad,the corrosion resistance of C4 is strong.The corrosion current was better than others by three orders of magnitude.There was a dissolution or transition of HA when the coatings are immersed in SBF.The addictive of particles can make the MAO coating smooth.CaHPO4·2H2O-doped coatings are smoothest.Thickness is in the range of 37 to 43?m.So particles have no effects on conductivity of the electrolyte.CaHPO4.2H2O and HA-doping do not change the phase composition,but the peak of Ti became weak.There was no CaHPO4-2H2O in the coatings,which indicating that CaHPO4·2H2O did not enter the granular coatings,but involved in chemical reactions.Ultrasonic cavitation can effectively improve the dispersion of the electrolytes,and the electrolytes dispersion can in favor of the uniform of the coatings.In the SBF immersion test,particle-doping has an impact on the capacity of inducing apatite.When CaHPO4·2H2O adding,there fine particles dispersed on the coating after immersion in SBF;when HA adding,there loose apatite dispersed on the coating after immersion in SBF.Larger amount of particles adding can induce apatite stronger.CaHPO4-2H2O-doped coatings have better corrosion resistance than that the HA-doped coatings.When the amount of CaHPO4·2H2O was 4g/L,the corrosion resistance of the coating could significantly be improved.The reseaon for apatite-forming ability in SBF is that abundant Ti-OH groups were formed on the surfaces of the coatings during the SBF immersion process.Ti-OH reacts with the Ca2+ and PO43-,promoting the growth of the nucleation of apatite.